Lens driving apparatus and optical pickup unit having the same

1. A lens driving apparatus comprising: a first lens-barrel having a lens built thereinto; a second lens-barrel; an electromechanical conversion element that applies a driving force f 1 to the first lens-barrel and a driving force f 2 to the second lens-barrel; and a housing that supports the lateral surfaces of the first lens-barrel and the second lens-barrel such that a lens-barrel body is mounted slidably on the housing in the light axis direction of the lens, the lens barrel body being the first lens-barrel and the second lens-barrel connected via the electromechanical conversion element therebetween, wherein the electromechanical conversion element generates deformation which results in displacement in the light axis direction of the lens by applying a drive voltage, and wherein the first lens-barrel generates an inertia force IF 1 and a friction force FF 1 with the support surface of the housing by applying the driving force f 1 , and wherein the second lens-barrel generates an inertia force IF 2 and a friction force FF 2 with the support surface of the housing by applying the driving force f 2 , and wherein the lens-barrel body is driven to one side in the light axis direction of the lens, such that a relationship of f 1 <IF 1 +FF 1 as well as f 2 >IF 2 +FF 2 holds, when the electromechanical conversion element generates the deformation so as to increase an interval between the first lens-barrel and the second lens-barrel, and such that a relationship of f 1 >IF 1 +FF 1 as well as f 2 <IF 2 +FF 2 holds, when the electromechanical conversion element generates the deformation so as to reduce an interval between the first lens-barrel and the second lens-barrel, and wherein the lens-barrel body is driven to the other side in the light axis direction of the lens, such that a relationship of f 1 >IF 1 +FF 1 as well as f 2 <IF 2 +FF 2 holds, when the electromechanical conversion element generates the deformation so as to increase an interval between the first lens-barrel and the second lens-barrel, and such that a relationship of f 1 <IF 1 +FF 1 as well as f 2 >IF 2 +FF 2 holds, when the electromechanical conversion element generates the deformation so as to reduce an interval between the first lens-barrel and the second lens-barrel.

2. The lens driving apparatus of claim 1 , wherein the electromechanical conversion element is a piezoelectric element to be expanded and contracted in the thickness direction along the light axis direction of the lens by applying the drive voltage.

3. The lens driving apparatus of claim 1 , wherein a guide groove is formed to dispose the lens-barrel body in the housing and to support the lens-barrel body slidably along the guide groove.

4. The lens driving apparatus of claim 3 , wherein the guide groove is formed with a substantially V-shaped cross section to support the lens-barrel body along two predetermined bus lines of the lens-barrel body on the wall surfaces of the guide groove.

5. The lens driving apparatus of claim 1 , wherein when it is assumed that m 1 and m 2 are the mass of the first lens-barrel including the lens and the mass of the second lens-barrel, respectively, and that μ 1 and μ 2 are maximum friction coefficients when the first lens-barrel and the second lens-barrel sliding on the support surfaces supported by the housing, respectively, a relationship of m 1 >m 2 as well as μ 1 <μ 2 holds.

6. The lens driving apparatus of claim 5 , wherein the support surface of the first lens-barrel supported by the housing is finished smoother than the support surface of the second lens-barrel supported by the housing.

7. The lens driving apparatus of claim 5 , wherein the support surface of the second lens-barrel supported by the housing is finished rougher than the support surface of the first lens-barrel supported by the housing.

8. The lens driving apparatus of claim 5 , wherein the material of the first lens-barrel is metal and the material of the second lens-barrel is plastic.

9. An optical pickup unit, wherein the lens driving apparatus of claim 1 is disposed on a light path between a laser light source and an objective lens, and wherein the lens built into the first lens-barrel of the lens driving apparatus is an aberration correction lens that corrects spherical aberration generated by a light emitting optical system which guides laser light to a signal recording medium, and wherein the spherical aberration of a condensed spot of the laser light which is irradiated on a signal layer of the signal recording medium, is corrected displacing the aberration correction lens in the light axis direction by driving the lens-barrel body.